A numerical simulation for the omega band formation
A numerical simulation for the omega band formation
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欧米茄能带形成的数值模拟
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发表时间：
2011
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通讯作者：
Tetsuya T. Yamamoto
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文献类型：
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作者：
Tetsuya T. Yamamoto
[1]数值模拟了亚暴恢复过程中欧米伽带和火炬结构的形成。极光粒子的动能基本上是由尾电流片中的非绝热加速提供的。等离子体片离子的磁漂移通量（在绝热意义上）随着不变纬度的降低而增加;它开始在一定的磁壳周围显着增加，这是假设的，作为一个第一近似，是分界的非绝热和绝热区域的尾电流片的接口。在该界面相对于平均磁漂移速度方向倾斜的情况下，可以产生区域1场向电流。只要注入粒子的能量密度不随时间显著变化，区域1电流保持稳定，并且没有长波长（在电离层高度>100公里）的静电波增长。由于非绝热粒子加速被假定为在亚暴的（早期）恢复阶段减弱，注入粒子的通量管积分能量密度达到混合Kelvin-Helmholtz/Rayleigh-Taylor不稳定性的纬向分布不稳定。当注入的动能较小的粒子被输送到低纬度的磁壳层时，不稳定区域在纬度上扩大，从而在等离子体片中形成长波长波。然后，欧米茄带类似于那些通常观察到的亚暴恢复阶段的形式。模拟中的欧米茄带的主要特征与观测结果一致。
[1] The formation of the omega bands and torch structures in the recovery phase of a substorm is numerically simulated. The kinetic energies of auroral particles are substantially provided by nonadiabatic acceleration in the tail current sheet. The magnetic drift flux (in the adiabatic sense) of the plasma sheet ions increases with decreasing invariant latitude; it starts to increase significantly around a certain magnetic shell, which is assumed, as a first approximation, to be the interface demarcating the nonadiabatic and adiabatic regions in the tail current sheet. Region 1 field-aligned currents can be generated in the situation that this interface is inclined with respect to the direction of the average magnetic drift velocity. As long as the energy density of injected particles does not significantly change with time, the region 1 current remains stable and no electrostatic waves with long wavelengths (>100 km at the ionospheric height) grow. Since the nonadiabatic particle acceleration is assumed to weaken during the (early) recovery phase of a substorm, the flux-tube-integrated energy density of injected particles attains a latitudinal profile unstable to the hybrid Kelvin-Helmholtz/Rayleigh-Taylor instability. While injected particles with less kinetic energies are transported to magnetic shells at lower latitudes, the unstable region expands in latitude so that long-wavelength waves develop in the plasma sheet. Then omega bands similar to those observed commonly in the substorm recovery phase form. The main characteristics of the omega bands in the simulation are shown to be consistent with observations.